Tooth loss is still prevalent not only due to neglect by the individual, but even in some patients who regularly seek dental treatment. Many factors play a role in the loss of teeth, including the cost of extensive restorative work not affordable for some individuals. The importance of simple, long lasting restorations must be recognized as a preventative measure for tooth loss. However, the relatively short longevity of most common of restorations, especially those of resin based composite materials, results in frequently replacements. Replacement of restorations tends to result in an increased size of the new compared to the original restoration. Acid etched, beveled margins must be removed whenever etching is required for the new restoration. Thus, resin based materials may require the removal of more tooth structure than materials which are not dependent on retention created by acid etching. Only one study from UK published 15 years ago, have assessed the loss of tooth structure when amalgam restorations were replaced. It predicted that only 4-5 replacements of amalgam restorations would be possible due to increasingly larger restorations. No studies have been done to determine the increased size of composite restorations needing replacement. The present study will measure the loss of tooth structure in areas distant from the site of failure which caused the need for replacement. It will be carried out in a student clinic. If the results show a significant loss of intact tooth structure when restorations are replaced, the investigation will be extended to an R01 project and it will include experienced clinicians. The need for attention on "preventive restorative treatment" exists both in treatment of primary caries and when replacing failed restorations.